OBSERVATIONS ON THE OYSTERCATGHEB. 43 



be delivered obliquely into the cleft between the valves, and with- 

 out too much force, in order to avoid injury to either valve. 

 Rotation can be produced readily by a stroke made on the pos- 

 terior end of a shell, provided it is made above or below the 

 equator of the shell. 



The largest Mussel I have so far found opened by an Oyster- 

 catcher measured two inches in length by seven-eighths of an 

 inch in breadth (2 in. x f in.). But this was quite an excep- 

 tional size. The shell had been detached and opened through 

 the ventral fissure, and it showed no fracture. 



Shells ranging from one and three-eighths inches in length 

 by five-eighths of an inch in breadth (If x f ) to five-eighths by 

 five-sixteenths (f x T 5 g) are sometimes treated in a way that 

 differs from that ordinarily seen. The bird takes each shell in 

 turn without selection except as regards size. A small patch of 

 these Mussels may have the contents of every shell removed. 

 The shell is hammered open by the application of a rapid succes- 

 sion of forceful blows directed obliquely through the point of the 

 bill to the cleft between the valves, near the posterior end of the 

 hinge. The blows crush a portion of that valve which has the 

 more pressure to bear, and drive the fragments into the interior 

 of the shell. The bill is pushed home through the newly formed 

 opening, and is then employed, if necessary, to open up the shell 

 by any one of the ways I have already described. The method 

 can always be recognized at a glance by noting that there is no 

 preliminary inspection or tapping ; the bill is raised clearly off 

 the shell in the intervals of the succession of blows ; there is no 

 real downward progress until the final blow breaks the shell ; 

 there is an extraordinary hurry and display of brute force ; and 

 very often there is no laterally inclined or rotary leverage, as 

 the blows usually make a hole in the shell big enough to allow 

 of the whole contents being removed without separating the 

 valve3, or the leverage and scooping up of the contents are 

 combined in one operation. The peculiar manner of hammer- 

 ing the shell distinguishes this method from the more usual one 

 in which the bill is pushed home between the valves by a series 

 of thrusts without intermediate recoil, and in which leverage is 

 always requisite to open up the shell and allow of the contents 

 being removed. Shells which present the ventral border are 



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